CSCI 380: Operating Systems

Coins

Modify Coins.c to support half dollars, coins worth 50 cents.

• Add a new member to the struct
• Output "penny" if only one is needed. Use a const char * variable and conditional to do this.
• Test various inputs to ensure your logic is correct.

Queue

Your task is to modify the code in queue.h and queue.c to fully implement the following functions.

• q_new: Create a new, empty queue.
• q_free: Free all storage used by a queue.
• q_insert_head: Attempt to insert a new element at the head of the queue (LIFO discipline).
• q_insert_tail: Attempt to insert a new element at the tail of the queue (FIFO discipline).
• q_remove_head: Attempt to remove the element at the head of the queue.
• q_size: Compute the number of elements in the queue.
• q_reverse: Reorder the list so that the queue elements are reversed in order.

Prelude

• Create a character array of size 80 for the string buffer. Declare the array size as a CONSTANT.
• Use fork to create a new process. See the fork example and the man page (i.e., man 2 fork).
• Read the string ensuring you do NOT allow a buffer overflow. Investigate fgets, strtok, and strcspn.
• Use getpid to obtain a PID. You may also find getppid helpful. Consult the man pages.
• Include header file <unistd.h>.

Output Format

shell> Hi there!
Parent says: PID = 1547, child PID = 1548, parent PID = 1237
Child says:  PID = 1548, parent PID = 1547, 'Hi there!'

Prelude 2

Write a simple shell that reads ONE command, forks a process to execute the command, and waits for the command to complete before printing its exit status.

• Print a prompt and read a command string from the user, which MAY include spaces.
• Tokenize the string, creating an args array. You may assume the string is not empty. Use space, tab, and newline characters as delimiters.
• Fork a process, ensuring you detect and print errors. Use strerror as you did before.
• In the child process, execute the command using execvp. (A variant of execve that omits the environment and searches in your path for the executable.)
• In the parent process wait for the child to terminate using waitpid (i.e., reap the child). Print the exit status with WEXITSTATUS.

Output Format

shell> ls -a
[ ls ] (PID: 3052378)
.             Descr.c                       MallocLab
..            Dest.txt                      Midterm.txt
a             Dir                           Notes
...
[* ls *] (Exit: 0)